1. Field of the Invention
The invention is a recirculating optical/electronic closed loop process and apparatus in which nanosecond light pulses are repetitively passed through a light-transparent medium to test the time delay caused by a changing refractive index in the medium and to indicate any needed change in the constituency of the medium.
2. Description of the Prior Art
In process control technologies, there is a wide-spread need for a sensing data and apparatus which meaures and records optical density of materials or measures small distance variations between two or more reference points. The process control has application in fluid control devices or systems which, as examples, record the transmittance or the fluid level in vessels, determine the refractive index of such liquids, and replace displacement measuring devices that are predominantly used in the tool machine industry. In the past, level meters have ued complicated mechanical apparatus, refractometers have used optical devices with read-out techniques that depend on human obervers, and the displacement of materials was often recorded manually or semi-automatically by applying a measuring stick or tape or by some electrical read-out gadget. There is a need for obtaining minute changes in the detected data on the refractive index, over wide ranges of refractive index changes, represented as n+.DELTA.n, in light-transparent media. These refractive index changes may be used in controlling various process control operations.